Streaking is a term of art used to describe a particular surface cosmetic defect in a molded part. It is believed that this defect which appears as striations in molded pigmented resins results from poor dispersion of the pigment. Moldings prepared from flame retardant, pigmented polycarbonates were noticed to exhibit a particularly objectionable degree of streaking if PTFE was used as a drip suppressant in the composition. As is described below, the art sought the means to alleviate the defect yet no solutions proposed hitherto were completely satisfactory.
U.S. Pat. No. 4,049,614 discloses polycarbonate molded articles containing pigments where silica was used to improve the surface appearance, i.e., to provide color homogeneity throughout the surface. U.S. Pat. No. 3,360,498 discloses polycarbonate compositions containing silica powder having a treated surface. The compositions are said to exhibit an improved level of hydrolytic and thermal stability as well as abrasive and solvent resistance. Thermally stable translucent polycarbonate compositions containing a mixture of poly(dimethylsiloxane) gum and finally divided silica have been disclosed in U.S. Pat. No. 3,933,730.